According to the invention, a buckle tensioner for pre-tensioning a safety belt band comprises a traction transmission device engaging on a belt buckle, a motor and a pressure storing device which is able to be compressed by means of the motor. The traction transmission device is coupled in a force-fitting manner to the pressure storing device and the pressure storing device is arranged such that an expansion of the pressure storing device brings about a pulling away of the belt buckle for tensioning the safety belt band. In contrast to the known buckle tensioner, the motor is not used for the actual pre-tensioning process, but rather serves for the previous compression of the pressure storing device. The expansion of the pressure storing device is used for the pre-tensioning process. As the compression of the pressure storing device is non-critical with respect to time and only has to be repeated possibly after an actual pre-tensioning process, a simple motor can be used for this. The only prerequisite is that the motor provides the torque necessary for compressing the pressure storing device. The pressure storing device preferably comprises a helical spring, but a pressure storing device which works with a compressible fluid (pneumatic or hydraulic pressure reservoir) can also be used.
The motor is preferably constructed so as to be self-locking, so that after the compression of the pressure storing device by the motor, no further steps are necessary in order to keep the pressure storing device in its compressed state. Alternatively, however, the pressure storing device can also be kept in a compressed state by a locking device.
In the preferred embodiment of the invention, the expansion of the pressure storing device is brought about by a trigger device which is able to be activated by the motor. Therefore, the motor has a dual function: Firstly, it is used for compressing the pressure storing device, to set the buckle tensioner into the state ready for operation; secondly, if required in a precrash situation, it activates the trigger device. This saves additional components which would otherwise be necessary for triggering the pre-tensioning process.
Preferably the pressure storing device is compressed by means of a longitudinally displaceable first rack, driven by the motor. According to the preferred embodiment of the invention, the motor is coupled to a pinion which engages into first teeth of the first rack, the latter being brought out of engagement with the pinion by activation of the trigger device. Thus, the compressed pressure storing device can be released in a simple manner to carry out the pre-tensioning process.
A particular advantage is produced in that the trigger device comprises a trigger piece movably supported on the first rack and coupled to a second rack having teeth which are constructed so as to be complementary to second teeth of the first rack, the second teeth of the first rack being brought into engagement with the teeth of the second rack on activation of the trigger device, and the racks being arranged such and the profiles of the teeth of the racks being constructed such that a relative displacement of the second rack with respect to the first rack brings the first teeth of the first rack into engagement with the pinion again. Such a construction makes it possible after a pre-tensioning process to return the tensioner mechanism in a simple manner into a state in which the pressure storing device can be compressed again, so that the buckle tensioner is available for a further pre-tensioning process.
For the emergency tensioning, following the pre-tensioning in an actual accident, according to a further development of the invention a pyrotechnic device is provided, which is coupled to the buckle tensioner such that through the pyrotechnic device a further tensioning is achieved which goes beyond that obtained through the expansion of the pressure storing device.